1. Field of the Invention
The present invention relates to a detection apparatus for detecting the process end point in a process of forming a layer on a semiconductor wafer, or a process of removing the layer on a wafer, such as a polishing process, in a process of manufacturing a semiconductor device such as an integrated circuit; a detection method; a polishing apparatus; a method for manufacturing a semiconductor device; and a recording medium on which is recorded a detection method program.
2. Discussion of the Related Art
The trend toward higher density in semiconductor devices is continuing with no end in sight, and various techniques and methods are being developed in an effort to achieve higher density. One of these is multilayer wiring, and related technological issues include the planarization of a global device face (over a relatively large area) of a semiconductor wafer, and wiring between upper and lower layers.
Taking into account the reductions in exposure light wavelength in lithography, as well as the reductions in focal depth during exposure attendant to high NA (Numerical Aperture), there is a great need for precision in the planarization of interlayers, at least around the exposure area. There is also a great need for so-called inlaying (plugging, damascene process), in which a metal electrode layer is inlaid in order to achieve multilayer wiring, in which case any extra part of the metal layer must be removed and planarized after the lamination of the metal layer. A polishing process called CMP has been remarked as an efficient technique for planarizing large areas. CMP (Chemical Mechanical Polishing or Planarization) makes use of both a physical polishing action and a chemical polishing action (dissolving out with a solution of a polishing agent), and is the best candidate for a technique that will allow global planarization and electrode formation in the process of removing the surface layer of a wafer. In specific terms, polishing agents called slurry are produced by dispersing polishing grit (generally silica, alumina, cerium oxide, or the like) in acid, alkali, or another solvent capable of dissolving the material to be polished, and using this slurry, pressure is applied to the wafer surface with a suitable polishing pad, and polishing is carried out by rubbing with relative motion. Uniform polishing within a plane is possible by keeping the pressure and relative motion speed constant over the entire wafer surface.
FIG. 12 is a simplified diagram of a conventional CMP polishing apparatus. A wafer 2 placed on a polishing head 1 is pressed against a polishing pad 3 while rotating at an angular velocity ùH. A platen 4 to which the polishing pad is fixed rotates at an angular velocity ùH. A polishing agent (slurry) 17 is supplied in between the wafer 2 and the polishing pad 3 from a polishing agent supply equipment 16, and the polishing surface of the wafer 2 is polished by the chemical and mechanical actions of the slurry 17 and the polishing pad 3. The polishing velocity v at any point within the wafer 2 plane is expressed by v=rC·ωT−rH·(ωH−ωT) (where rC is the distance from the center of the platen 4 to the center of the polishing head 1, and rH is the distance from the center of the polishing head 1 to the polishing point). Therefore, when ωH=ωT, the polishing rate is constant regardless of the position within the wafer 2.
An important requirement in this process is the detection of the end point of the polishing process. Detecting the polishing end point while the polishing process is underway (in-situ) is especially important in terms of process efficiency.
As to this detection method, a standard film thickness measurement apparatus is frequently used to detect the end point of the polishing process. Detection and measurement are performed by a variety of methods, selecting a microscopic blank portion of the washed wafer after the process (the places without a device pattern) as the measurement site.
A faster monitoring method in the polishing and planarizing process is to detect the frictional fluctuations when the polishing moves to another layer than the layer that is supposed to be polished, by means of the changes in the motor torque of the wafer rotation or pad rotation.
In addition, there is a method in which the wafer face is irradiated with laser light, and the film thickness is measured by utilizing optical interference to track fluctuations in the reflected light intensity over time. There are numerous methods in which changes in intensity are tracked over time and the end point is deemed to be the point when a specific value is reached, but because of effects such as signal noise and error in the measurement position and uncertainty dependent on the device pattern of the wafer, it is considered to be difficult to clearly determine the process end point.
There are various methods for detecting the end point in a CMP process, as discussed above, but a method that can be considered definitive has yet to be found.
For instance, measurement with a film thickness measurement apparatus does provide sufficient precision and reliable data, but the apparatus itself is bulky, measurement takes a long time, and feedback to the process is slow.
A method in which the process end point is detected from motor torque is convenient and fast, but it is only effective in detecting the process end point when there is a clear change in the layer to a different type; furthermore, its precision is inadequate.
Meanwhile, a method in which the wafer face is irradiated with laser light is hampered by error in the measurement position and uncertainty dependent on the type of device pattern of the wafer, and by the effect of signal noise originating in the slurry and so on, and these combine to disturb the signal, so it is held to be difficult to clearly determine the process end point.
The present invention solves the above-mentioned problems and provides an apparatus for detecting the polishing end point, with which this point can be detected simultaneously with the polishing (in-situ) even when the signal is disturbed and when the polishing layer does not clearly change to a different type; a detection method; a polishing apparatus; a method for manufacturing a semiconductor device; and a recording medium on which is recorded a detection method.